1. Field of the Invention
The present invention relates to a photoresist superior in resolution, sensitivity and contrast with a high glass transition temperature and, more particularly, to a photoresist using dioxaspiro ring-substitued acryl derivatives.
2. Description of the Prior Art
There have been developed extensive photoresists. Conventional photoresists typically comprise an alkali-soluble phenol-(or cresol-) formaldehyde novolak resin as a binder and substituted naphthoquinone diazide as a photosensitive material, as disclosed in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. While the novolak resin is dissolved in an aqueous alkali solution, the naphthoquinone compound plays a role as a dissolution inhibitor. If a substrate coated with this photoresist is selectively exposed to a light beam, the photosensitive material is altered in structure so that the exposed regions of the photoresist coating are more soluble than the unexposed regions. When the substrate is immersed in an aqueous alkali solution, the exposed regions are dissolved at a faster rate with the unexposed regions being etched at a slower rate, resulting in the formation of a relief pattern on the substrate.
With the advance in lithography, the light source is selected from a region of deep ultraviolet which ranges, in wavelength, from 200 to 300 nm. In this light region, however, the naphthoquinone photosensitive material exhibits too great light absorption in addition to being of low sensitivity. Therefore, there has been a demand for the development of novel photoresists capable of effectively functioning in the light.
The novel photoresists are required to be superior in photosensitivity, contrast, resolution and etch resistance. Of them, photosensitivity is the most important. In order to enhance the photosensitivity, there was introduced a chemical amplification concept. In the chemical amplification, the active species generated by a photochemical reaction serves as a catalyst which allows chemical reactions, such as deprotection and crosslinking, to occur continuously, so that the total yield of protons in these reactions is greatly amplified relative to the initial proton yield of the catalyst.
Accordingly, a great interest has recently been taken in chemical amplification-type photoresists to achieve the high sensitivity necessary for the lithography in semiconductor fields. Representative, most powerful resins are t-butoxycarbonyl-protected polyvinylphenols, as reported in U.S. Pat. Nos. 4,311,782, 4,405,708 and 4,491,628. In fact, the resins were found to enhance sensitivity by 100 times greater than do conventional positive novolak photoresists.